It has been conventional in track chain constructions to utilize coaxial pins and bushings extending between the parallel track chain adapted to have meshing engagement with the sprocket of the tractor drive so as to propel the tractor by means of the track assembly. Such construction required fixation of the ends of the bushing in the opposite track chain links and problems have arisen from time to time in maintaining the securing of the bushing ends therein. Further, the pins which provide the articulation of one link to the other in the track chain assembly have presented problems in requiring lubrication and maintain axial positioning. Further, the use of such pin and bushing sprocket means has caused the weight of the track chain construction to be relatively large.
An example of an improved cartridge joint for a heavy duty track chain having fork and blade-type track links and a midpitch drive lug is shown in U.S. Pat. No. 3,601,454 of Harold L. Reinsma, which patent is owned by the assignee hereof. The use of the cartridge joint produced greater strength in the connection of the links at a reduced cost and permitted facilitated replacement in the field.
In U.S. Pat. No. 3,829,173, which patent is owned by the assignee hereof, Robert N. Stedman disclosed a track assembly utilizing fork and blade-type links pivotally mounted together by a tubular pin and a pair of annular bearings. The assembly includes an annular seal and a retaining means disposed on the outboard side of the bearings.